The present invention relates to the recognition of tissue types in human subjects, and, in particular, to such recognition being performed by way of impedance measurements of the electrical properties of tissue.
Various arrangements have been described that employ electrical measurements on tissue to derive a diagnosis of the nature of that tissue. Such diagnosis typically relates to the detection of cancerous or pre-cancerous tissue.
For the most part, previous attempts to use electrical measurements for tissue diagnosis have suffered from low performance, as measured by their combined sensitivity and specificity. The measurement of absolute levels of conductivity, for example, has been unreliable through the presence of uncontrolled variability in electrode characteristics. Such variability can occur both over the course of time or between different batches of electrodes.
Previous attempts to use tissue impedance for the detection of cancerous tissue on a patient""s surface have not been successful because such have primarily measured the bulk impedance. This has been particularly the case with cervical cancer, which is neoplasia, typically of the upper ten or so cells of the tissue surface being examined.
It is an object of the present invention to substantially overcome, or at least ameliorate, one or more deficiencies with prior arrangements.
In accordance with one aspect of the present disclosure there is provided a method of tissue-type recognition, said method comprising the steps of:
applying electrical signals to a tissue sample;
measuring from the applied signals a magnitude of impedance of the tissue and corresponding phase sample at each of a plurality of frequencies;
comparing at least the measured phase samples with phase information of known tissue-types taken at said frequencies; and
from said comparison, estimating to which of said known tissue-types said tissue sample corresponds.
In accordance with another aspect of the present disclosure, there is provided a method of tissue-type recognition, said method comprising the steps of:
applying electrical signals to a tissue sample at at least two frequencies from a range of frequencies;
measuring from the applied signals, at each of said at least two frequencies, a magnitude of tissue impedance and a phase of tissue impedance;
calculating a slope of phase versus frequency from said measured phases;
comparing at least said slope with phase slope information of known tissue-types over said range of frequencies; and
from said comparison, estimating which of said known tissue-types said tissue sample corresponds.
In accordance with another aspect of the present disclosure there is provided a method of determining a database for diagnosis of tissue types, said method comprising:
(a) for each of a plurality of tissue samples
(i) identifying a known tissue type of said sample;
(ii) taking at least phase measurements using electrical signals applied to said sample, said measurements comprising components at each of a plurality of frequencies.
(b) arranging the phase measurements at each said frequency into a group associated with each said known tissue type.
(c) processing the phase measurements in each said group to provide an processed phase value at each said frequency for each said tissue type.
(d) arranging the average phase measurements as a database.
Other aspects are also disclosed.
The arrangements described herein overcome the problems of making measurements at the tissue surface, whilst avoiding problems that can arise from variability in the surface characteristics of electrodes. These subtle surface characteristics can vary with time, between batches of electrodes and because of contamination by body fluids of the patient, for example due to protein absorption These surface changes can lead to changes in the electrical capacitance of the electrodes measured from the impedance data. Even the mere application of an electrical potential to the electrodes can alter their properties so as to make diagnosis unreliable unless appropriate corrections are made.